Field
Some embodiments are related to a metal oxide material useful in breath gas analysis. Some embodiments are related to medical devices which analyze human breath to determine health conditions. Some embodiments are related to methods of detecting acetone to determine the presence of health conditions, such as diabetes.
Description of the Related Art
Scientists have discovered connections between certain illnesses and physical conditions that are associated with the presence of certain gases in mammalian expiratory breaths. Some scientists have even linked the detection of acetone in human breath to illness such as diabetes. M. Righettoni & A. Tricoli, Toward Portable Breath Acetone Analysis for Diabetes Detection, 5(3) J. Breath Res. (2011). To that end, gas sensing devices have been reported. United States Patent Publication 2009/0054799 (Pub. 26 Feb. 2009), United States Patent Publication 2010/0077840 (Pub. 1 Apr. 2010), United States Patent Publication 2013/0115706 (Pub. 9 May 2013).
In the art of gas sensors, tungsten oxide is one of the materials that can be used in gas sensors. Tungsten Oxide (WO3) crystals can be formed by corner and edge sharing of WO6 octahedra. Various phases can be obtained by corner sharing, e.g., monoclinic II (epsilon [ε]-phase); triclinic (delta [δ]-phase), monoclinic I (gamma [γ]-phase), orthorhombic (beta [β]-phase), tetragonal (alpha [α]-phase), and cubic WO3. The monoclinic II phase has been reported as generally stable only at subzero temperatures, with monoclinic I as the most stable phase at room temperature. H. Zheng, et al., Nanostructured Tungsten Oxide—Properties, Synthesis, and Applications, 21 Adv. Funct. Mater. 2175-2196 (2011). E-phase tungsten oxide has been described as useful for gas sensors. M. Righettoni & A. Tricoli, supra. While scientists have explored doping of tungsten oxide to improve its performance, doping has only used noble metals, Si, V, Cr, Cu, CuO, and VPO, see U.S. Pat. No. 8,980,640 (17 Mar. 2015); I. Jiménez, NH3 Interaction with Catalytically Modified Nano-WO3 Powders for Gas Sensing Applications, 150(4) J. Electrochem. Soc. H72-H80 (2003); L. Wang at al., Ferroelectric WO3 Nanoparticles for Acetone Selective Detection, 20 Chem. Mater. 4794-4796 (2008); M. Righettoni et al., Breath Acetone Monitoring by Portable Si:WO3 Gas Sensors, 738 Anal Chim Acta 69-75 (13 Aug. 2012); S. Kanan, et al., Semiconducting Metal Oxide Based Sensors for Selective Gas Pollutant Detection, 9 Sensors 8159, 8162 (2009); A. Rydosz et al., Deposition of Nanocrystalline WO3 and CuO Thin Film in View of a Gas Sensor Applications, Society of Digital Information and Wireless Communications (SDIWC): The Second International Conference on Technological Advances in Electrical, Electronics and Computer Engineering (TAEECE2014) Proceedings 150-55 (March 2014).
Even with advances, metal oxide gas detectors still require the use of heaters to meet operating temperature requirements. M. Righettoni & A. Tricoli, supra. Silicon-doped epsilon-phase (ε or Epsilon) WO3 is a nano metal oxide acetone sensing material, but it is described as working from about 300° C. to about 400° C., a potentially difficult temperature to attain in a portable device without the addition of a heater. M. Righettoni et al., supra. In addition, operating temperatures near 400° C. or above can have adverse effects upon the sensing material, e.g., changing the phase of some of the material.
Despite advances, there is still a need for an acetone sensor that provides efficient gas detection for use in portable devices that could be used for diagnosis and self-monitoring of outpatients having various physical conditions, including diabetes.